The present invention pertains to noninvasive eye-property monitoring, and more particularly to the noninvasive monitoring of various eye properties through noting how, in an observed light reflection from the eye, certain characteristics of selected and controlled light which has been directed toward the eye have become affected in the process of the directed light's engagement with the eye. While there are many useful applications for the practice of this invention, I have found that its methodology offers particular, and notably high, utility in relation to the monitoring of aqueous-humor glucose content as an indication of blood glucose level— an important, medically-associated diagnostic task. Consequently, while practice of the invention involves the broader concept of using specially created and controlled eye-directed, and resulting eye-reflected, light in the practice of looking at various eye properties, both for assessing these properties as end results in and of themselves, and additionally for using these detected properties as related indicators of other physical conditions, a preferred and best-mode system for, and manner of, practicing the invention are illustrated and described herein specifically in the mentioned high-utility setting of glucose monitoring through examining how the presence of glucose in the aqueous humor (the aqueous) effects certain interactions with certain characters of light. Such effecting results from what is referred to herein as optical activity, and an illustration of optical activity is a change in qualities of light reflection from the eye.
Other, representative (non-exhaustive) eye “properties” associated with the aqueous humor, known to be of interest, and regarding which the invention may be employed, include uric acid, ascorbate, lactic acid, inorganic phosphates, bicarbonates, chlorides, and urea.
Moving along now, and considering the topic of glucose, maintaining an appropriate concentration of glucose in the blood is critical for reducing the likelihood of complications from diabetes mellitus. Currently, blood glucose concentration is usually measured by extracting a drop of blood and subjecting it to a form of chemical analysis.
It would obviously be preferable to be able to measure blood glucose concentration non-invasively. However; many constituents of blood and skin other than glucose have so far prevented the successful development of an instrument to measure blood glucose through the skin.
There is good evidence that the concentration of glucose in the aqueous humor of the eye varies with blood glucose concentration, with a lag of about ten minutes. Further, the aqueous humor contains far fewer confounding components than does blood, and it lies behind transparent tissue, the cornea, instead of being shielded by skin. Therefore, attempting to measure glucose concentration in the aqueous, as I have found, has promise for providing a non-invasive measure of blood glucose level.
When the glucose concentration in the aqueous changes, the index of refraction of the aqueous changes proportionately. Further, the amount of change in the index is different for different wavelengths of light. When light is reflected from an interface between two partially transparent substances, the proportion of incident light that is reflected depends upon the ratio of the indices of refraction of the two substances. Therefore, if the glucose concentration in the aqueous changes, the intensity of light reflected from the interface between the back surface of the cornea and the aqueous will change, and the change will be different for different wavelengths.
Regarding another useful phenomenon, when light passes through the aqueous humor, an amount of it is absorbed that depends upon the wavelength of the light involved, and the amount of glucose in the aqueous humor.
As will be seen, the system and methodology of the present invention, in the illustrative glucose-detection/monitoring setting described below, produce information contained in light-associated, optical-activity-affected, reflected light which furnishes a measure of aqueous glucose concentration— which information may be based upon either changes in index of refraction or of absorption or both. With appropriate calibration, it makes no difference which, or whether both, of these two optical phenomena contribute to this information. Such calibration may be performed by conducting a conventional blood glucose concentration test, and then, essentially at the same time, implementing eye-reflection-condition monitoring in accordance with the invention to compare data.
According to one way of expressing the invention, based upon considering the invention in its broader aspects, what is proposed is an eye-property monitoring system and methodology collectively featuring the enabling and practicing of the steps including (1) illuminating the eye from at least one light source whose wavelength interacts with internal eye properties in an optically active manner, (2) controlling, to make substantially known and stable, at a predetermined setting, the operating power/light-output level of the source, (3) by such illuminating, producing light-source eye reflections including (a) multiple internal reflections within the outer structure of the eye, and (b) at least one resulting outbound reflection, (4) monitoring the outbound-reflection to detect therein the reflection level associated with the at least one source, and (5) associating such detected reflection level as an indication of certain eye properties.
According to another, currently preferred and best-mode manner of practicing the invention, based upon the features and operation of the disclosed system of the invention, what is proposed is an eye-property monitoring method including (a) in a seriatim manner, illuminating the eye (one or more region(s) on the limbus) from two or more, different-wavelength light sources whose respective wavelengths interact with internal eye properties in optically differentiated manners, (b) adjusting the operating levels of the sources to a predetermined relative setting, (c) by such illuminating, producing seriatim-light-source eye reflections including multiple internal reflections within the outer structure of the eye, and at least one resulting outbound reflection, (d) monitoring the outbound-reflection to detect therein the relative reflection levels associated with the sources, and (e) associating such detected, relative reflection levels as an indication of certain eye properties.
According to still another, alternative, preferred and best-mode manner of practicing the invention utilizing its system, which manner expresses the invention in a more specific sense, proposed is a blood glucose monitoring method including (a) in an alternating manner, illuminating the eye (again, one or more region(s) on the limbus) from two, different-wavelength light sources, one of which has a wavelength to which glucose is more optically active than it is to the wavelength of the other source, (b) adjusting the operating levels of the two sources to a predetermined relative setting, (c) by such illuminating, producing eye reflections including multiple internal reflections within the outer structure of the eye, and at least one resulting outbound reflection, and (d) monitoring a selected condition of the outbound reflection as an indication of blood glucose level.
Even more specifically, the system-implementable methodology of the invention, as expressed in all three of the ways stated above, is preferably computer-based, and includes both (1) computer controlling of the illuminating, controlling and adjusting steps, and (2) computer conducting of the monitoring step. Illuminating is performed by directing light from the employed light sources along a common (in the case of two or more sources) illumination path which lies at an angle relative to the eye's line of sight, and the producing step is accomplished to effect eye reflections occurring within the cornea of the eye, and even more particularly is conducted so as to effect eye reflections, including multiple reflections, from the optical interface existing between the cornea (its inside, or back surface, or side) and the aqueous humor of the eye.
In thinking about this interface, it is interesting, and useful, to note that the inside surface of the cornea is completely covered, in a healthy eye, with a very thin layer of what are called endothelial cells. These cells may well affect the amount of light reflected at each cornea-reflection “bounce”, and so, a result, in terms of quantum mechanics, of such behavior is that photons meeting the inner surface of the cornea at a shallow angle (in a manner producing what is known in the relevant art as total internal reflection) will “tunnel” through the interface, and, if the properties of the endothelial cells are “right” (in a sense known to those skilled in the art), some of the associated light will escape the cornea (a phenomenon known as “frustrated total internal reflection”). Accordingly, if the thickness, or the index of refraction, or both, of the endothelial cells changes with glucose concentration, that will also affect monitoring measurement, and may do so perhaps beneficially, and maybe even strongly. Appropriate implementation-system calibration will take into account this potentially very useful phenomenon.
In the structural environment adjacent these endothelial cells, optical-reflection physics may actually be quite more complex than simple, in the sense that “internal-eye-structure” reflections produced by practice of the invention might include both (a) reflections from the optical interface existing between the cornea and the endothelial cells, and (b) reflections between the endothelial cells and the aqueous. It is also possible, in relation to monitoring glucose, that glucose concentration might affect the properties of the endothelial cells, for example in a manner, such as by cell-layer thickening, affecting reflection intensity. All of these considerations, however, complexities set aside from detailed analysis, will not affect the viability of invention practice with the earlier mentioned system calibration steps taken with respect to each examined person.
As will become evident, the optical, and associated computer-control, system which implements the methodology of the invention may be relatively simple in construction, and can readily lend itself to economical and compact construction—features which those skilled in the art will easily understand. Additionally, those skilled in the art will immediately recognize the possibilities for numerous variations in systemic and detailed methodologic practices that will lie well within the scope of the invention's basic contributions to the art, as expressed very generally above, and these matters testify to the important flexibility and versatility of the invention.
For examples, one can say, generally, about systemic and practice modifications which may readily be implemented by a user seeking to practice the methodology of the present invention in a manner best suited to the application chosen by that user, that they may include the following considerations.
While the system and methodology of the present invention are specifically illustrated and described herein principally in conjunction with the use of two, different-wavelength light sources, one should understand, and those skilled in the art will clearly appreciate, (a) that a greater number than two such sources may be employed, (b) that such sources may be designed to operate at wavelengths which differ from the specific wavelengths that are identified in text below, (c) that it is possible to use only a single wavelength, even with plural sources, if desired, and (d) that there may be applications wherein even only a single light source, operating, of course, at but a single wavelength, may be used. In all instances, it is important that chosen wavelengths, or a single chosen wavelength if that is what is to be employed, interact optically in a “noticeable” manner (as by experiencing changing eye-reflection characteristics) with the selected properties in the eye that are to be monitored so that light-impingement-produced reflection which is received and reviewed, in accordance with practice of the invention, will possess “reflection content” suitably indicative of the specific eye properties which are being examined. Those skilled in the relevant art will clearly appreciate these several matters.
With regard to the situation where plural light sources are employed, and more specifically where more than two such sources are used, the interrelating operations thereof, referred to as “seriatim” operations, may take place in various, user-selected patterns of energization.
Additionally, where plural light sources are used, the flow paths, or lines, along which incident illumination coming respectively from these sources need not exactly match one another, and while incident illumination should always strike a region on the limbus of eye, the incident beams need not necessarily strike exactly the same region of the limbus.
Yet another consideration is that, while the preferred and best-mode implementation of the invention specifically involves incident light being directed at an angle to the line of sight of the eye, it is entirely possible to consider illuminating the eye, and specifically a location on the limbus, along a line of illumination which may even parallel the line of sight. Important here is that light impingement be at a region on the limbus, and not more eye-centrally—a condition which might produce unwanted and interfering reflection(s) from the cornea.
Still a further consideration regarding what one skilled in the art choosing to implement the methodology of the present invention might consider doing involves suitably supporting the optical elements that are pictured and described herein on appropriate motor-driven support structure, under the control of the illustrated computer, for the purpose of automating precise positioning between these optical elements and a person's eye. There are many ways in which this kind of an arrangement might be made, all well within the conventional skills of those generally skilled in the relevant art, and accordingly, this area of “invention modification” is not specifically illustrated or further described herein.
These and various other features, advantages and possible modifications that characterize the present invention will become more fully apparent as the detailed description of it which follows below is read in conjunction with the accompanying drawings.
Various component sizes, and light-beam angles, that are pictured in these two drawing figures are not drawn, or presented, to scale